The aim of this project is to develop a new technology that can be used to detect very low concentrations (sub- picomolar) of proteins that are diagnostic for cancer. Presently, early diagnosis of cancer is limited by the fact that the limits of detections (LOD) of available technologies, such as ELISA, are higher than the circulating concentrations of low abundance proteins that could indicate the onset of disease. This program would establish the feasibility of using a novel fiber optic array single molecule detection technology for extremely high sensitivity measurement of cancer markers. This technology is digital in nature, i.e., individual molecules are quantified by their presence (on signal) or their absence (off signal). By focusing detection at the single molecule level, dramatic improvements in sensitivity on the order of 3-7 logs could be achieved for proteins. The project has two specific aims that would establish feasibility of the technique for detection of cancer protein markers. First, as the LOD of the technique is determined by the number of false }on} signals from non- specific events, surface chemistries will be developed to minimize or eliminate non-specific binding of biological molecules from a complex matrix such as human serum. These surface chemistries will incorporate immobilized antibodies that are used to specifically capture and detect low abundance target proteins. Second, the technological innovations in surface chemistry will be implemented to develop a high-sensitivity assay for prostate specific antigen (PSA), which is a marker for prostate cancer. This specific aim is intended to demonstrate that the fiber arrays technology can be used to follow levels of PSA several logs lower than present technology, thereby enabling prostatectomy patients to be assured that there is no residual disease. The long term objective of this research is to establish a new standard in high sensitivity detection of biological molecules (proteins, peptides, RNA, cells) using instrumentation that would be widely employed in both academic and clinical laboratories. Such an innovation would enable cancer researchers to detect cancer markers at unprecedented levels for early diagnostic applications, and would facilitate the discovery of new low abundance cancer markers. This long term goal satisfies several aspects of the mission of the NIH, in particular, to develop innovative research strategies towards improving the diagnosis, prevention and cure of human diseases.